.\"	$Id: mdoc.3,v 1.41 2010/05/30 22:56:02 kristaps Exp $
.\"
.\" Copyright (c) 2009-2010 Kristaps Dzonsons <kristaps@bsd.lv>
.\"
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.Dd $Mdocdate: May 30 2010 $
.Dt MDOC 3
.Os
.Sh NAME
.Nm mdoc ,
.Nm mdoc_alloc ,
.Nm mdoc_endparse ,
.Nm mdoc_free ,
.Nm mdoc_meta ,
.Nm mdoc_node ,
.Nm mdoc_parseln ,
.Nm mdoc_reset
.Nd mdoc macro compiler library
.Sh SYNOPSIS
.In mandoc.h
.In mdoc.h
.Vt extern const char * const * mdoc_macronames;
.Vt extern const char * const * mdoc_argnames;
.Ft "struct mdoc *"
.Fn mdoc_alloc "void *data" "int pflags" "mandocmsg msgs"
.Ft int
.Fn mdoc_endparse "struct mdoc *mdoc"
.Ft void
.Fn mdoc_free "struct mdoc *mdoc"
.Ft "const struct mdoc_meta *"
.Fn mdoc_meta "const struct mdoc *mdoc"
.Ft "const struct mdoc_node *"
.Fn mdoc_node "const struct mdoc *mdoc"
.Ft int
.Fn mdoc_parseln "struct mdoc *mdoc" "int line" "char *buf"
.Ft int
.Fn mdoc_reset "struct mdoc *mdoc"
.Sh DESCRIPTION
The
.Nm mdoc
library parses lines of
.Xr mdoc 7
input
into an abstract syntax tree (AST).
.Pp
In general, applications initiate a parsing sequence with
.Fn mdoc_alloc ,
parse each line in a document with
.Fn mdoc_parseln ,
close the parsing session with
.Fn mdoc_endparse ,
operate over the syntax tree returned by
.Fn mdoc_node
and
.Fn mdoc_meta ,
then free all allocated memory with
.Fn mdoc_free .
The
.Fn mdoc_reset
function may be used in order to reset the parser for another input
sequence.
See the
.Sx EXAMPLES
section for a simple example.
.Pp
This section further defines the
.Sx Types ,
.Sx Functions
and
.Sx Variables
available to programmers.
Following that, the
.Sx Abstract Syntax Tree
section documents the output tree.
.Ss Types
Both functions (see
.Sx Functions )
and variables (see
.Sx Variables )
may use the following types:
.Bl -ohang
.It Vt struct mdoc
An opaque type defined in
.Pa mdoc.c .
Its values are only used privately within the library.
.It Vt struct mdoc_node
A parsed node.
Defined in
.Pa mdoc.h .
See
.Sx Abstract Syntax Tree
for details.
.It Vt mandocmsg
A function callback type defined in
.Pa mandoc.h .
.El
.Ss Functions
Function descriptions follow:
.Bl -ohang
.It Fn mdoc_alloc
Allocates a parsing structure.
The
.Fa data
pointer is passed to
.Fa msgs .
The
.Fa pflags
arguments are defined in
.Pa mdoc.h .
Returns NULL on failure.
If non-NULL, the pointer must be freed with
.Fn mdoc_free .
.It Fn mdoc_reset
Reset the parser for another parse routine.
After its use,
.Fn mdoc_parseln
behaves as if invoked for the first time.
If it returns 0, memory could not be allocated.
.It Fn mdoc_free
Free all resources of a parser.
The pointer is no longer valid after invocation.
.It Fn mdoc_parseln
Parse a nil-terminated line of input.
This line should not contain the trailing newline.
Returns 0 on failure, 1 on success.
The input buffer
.Fa buf
is modified by this function.
.It Fn mdoc_endparse
Signals that the parse is complete.
Note that if
.Fn mdoc_endparse
is called subsequent to
.Fn mdoc_node ,
the resulting tree is incomplete.
Returns 0 on failure, 1 on success.
.It Fn mdoc_node
Returns the first node of the parse.
Note that if
.Fn mdoc_parseln
or
.Fn mdoc_endparse
return 0, the tree will be incomplete.
.It Fn mdoc_meta
Returns the document's parsed meta-data.
If this information has not yet been supplied or
.Fn mdoc_parseln
or
.Fn mdoc_endparse
return 0, the data will be incomplete.
.El
.Ss Variables
The following variables are also defined:
.Bl -ohang
.It Va mdoc_macronames
An array of string-ified token names.
.It Va mdoc_argnames
An array of string-ified token argument names.
.El
.Ss Abstract Syntax Tree
The
.Nm
functions produce an abstract syntax tree (AST) describing input in a
regular form.
It may be reviewed at any time with
.Fn mdoc_nodes ;
however, if called before
.Fn mdoc_endparse ,
or after
.Fn mdoc_endparse
or
.Fn mdoc_parseln
fail, it may be incomplete.
.Pp
This AST is governed by the ontological
rules dictated in
.Xr mdoc 7
and derives its terminology accordingly.
.Qq In-line
elements described in
.Xr mdoc 7
are described simply as
.Qq elements .
.Pp
The AST is composed of
.Vt struct mdoc_node
nodes with block, head, body, element, root and text types as declared
by the
.Va type
field.
Each node also provides its parse point (the
.Va line ,
.Va sec ,
and
.Va pos
fields), its position in the tree (the
.Va parent ,
.Va child ,
.Va next
and
.Va prev
fields) and some type-specific data.
.Pp
The tree itself is arranged according to the following normal form,
where capitalised non-terminals represent nodes.
.Pp
.Bl -tag -width "ELEMENTXX" -compact
.It ROOT
\(<- mnode+
.It mnode
\(<- BLOCK | ELEMENT | TEXT
.It BLOCK
\(<- HEAD [TEXT] (BODY [TEXT])+ [TAIL [TEXT]]
.It ELEMENT
\(<- TEXT*
.It HEAD
\(<- mnode+
.It BODY
\(<- mnode+
.It TAIL
\(<- mnode+
.It TEXT
\(<- [[:printable:],0x1e]*
.El
.Pp
Of note are the TEXT nodes following the HEAD, BODY and TAIL nodes of
the BLOCK production: these refer to punctuation marks.
Furthermore, although a TEXT node will generally have a non-zero-length
string, in the specific case of
.Sq \&.Bd \-literal ,
an empty line will produce a zero-length string.
Multiple body parts are only found in invocations of
.Sq \&Bl \-column ,
where a new body introduces a new phrase.
.Sh EXAMPLES
The following example reads lines from stdin and parses them, operating
on the finished parse tree with
.Fn parsed .
This example does not error-check nor free memory upon failure.
.Bd -literal -offset indent
struct mdoc *mdoc;
const struct mdoc_node *node;
char *buf;
size_t len;
int line;

line = 1;
mdoc = mdoc_alloc(NULL, 0, NULL);
buf = NULL;
alloc_len = 0;

while ((len = getline(&buf, &alloc_len, stdin)) >= 0) {
    if (len && buflen[len - 1] = '\en')
        buf[len - 1] = '\e0';
    if ( ! mdoc_parseln(mdoc, line, buf))
        errx(1, "mdoc_parseln");
    line++;
}

if ( ! mdoc_endparse(mdoc))
    errx(1, "mdoc_endparse");
if (NULL == (node = mdoc_node(mdoc)))
    errx(1, "mdoc_node");

parsed(mdoc, node);
mdoc_free(mdoc);
.Ed
.Pp
Please see
.Pa main.c
in the source archive for a rigorous reference.
.Sh SEE ALSO
.Xr mandoc 1 ,
.Xr mdoc 7
.Sh AUTHORS
The
.Nm
library was written by
.An Kristaps Dzonsons Aq kristaps@bsd.lv .
